The present invention relates to a detection apparatus capable of detecting the position of an object or the like at high precision, an exposure apparatus having the detection apparatus, and a device manufacturing method using the detection and exposure apparatuses. The present invention is preferable when the position of an object such as a wafer is detected at high precision by observing an image on the object, and the object is aligned based on the detection information in an exposure apparatus for manufacturing various devices such as a semiconductor IC, LSI, CCD, liquid crystal panel, and magnetic head.
Along with the recent remarkable development of semiconductor element manufacturing techniques, the progress of micropatterning techniques is also prominent. As an optical processing technique, reduction projection exposure apparatuses generally called steppers having submicron resolutions are mainstream. For higher resolutions, a larger numerical aperture (NA) of an optical system and a shorter exposure wavelength are being realized.
As the exposure wavelength decreases, the exposure light source is shifting from high-pressure mercury lamps of g-line and i-line to KrF and ArF excimer lasers.
As the resolution of a projection pattern increases, high precision is also demanded for relative alignment between a wafer and a mask (reticle) in a projection exposure apparatus. The projection exposure apparatus needs to function not only as a high-resolution exposure apparatus but also as a high-precision position detection apparatus.
For this purpose, high performance is required for a position detection apparatus, also called an alignment scope, for detecting an alignment mark on a substrate such as a wafer.
As the form of the alignment scope, there are roughly proposed two methods. One form of an alignment scope is a so-called off-axis alignment detection system (Off-Axis AA; to be simply referred to as an xe2x80x9cOAxe2x80x9d hereinafter), which is separately disposed without the mediacy of a projection exposure optical system and optically detects an alignment mark.
The other one of the conventional methods is a method of detecting an alignment mark on a wafer by using the alignment wavelength of non-exposure light via a projection optical system called a TTL-AA (Through The Lens Automatic Adjustment).
In either alignment scope, the aberration of the alignment scope generates a position detection error. This aberration must be minimized, or the generated aberration must be corrected.
A projection exposure optical system having a conventional OA detection system will be described with reference to the schematic view of FIG. 3.
Light IL emitted by an exposure illumination optical system 1 including an exposure light source (as the light source, a mercury lamp, a KrF excimer laser, an ArF excimer laser, or the like may be used) illuminates a mask (reticle) 2 having a pattern. At this time, the reticle 2 is aligned in advance by reticle holders 12 and 12xe2x80x2 such that an alignment detection system 11 above (or below) the reticle 2 makes the center of the reticle pattern coincide with an optical axis AX of a projection exposure optical system 3.
The light having passed through the reticle pattern transfers the image of the reticle pattern onto a wafer 6 held on a wafer stage 8 at a predetermined magnification via the projection exposure optical system 3. Note that an exposure apparatus for irradiating the reticle 2 with irradiation light from above the reticle 2 and sequentially exposing the wafer 6 to reticle pattens at a fixed position is called a stepper. An exposure apparatus for relatively moving the reticle 2 and wafer 6 (the moving amount of the reticle 2 is the product of the moving amount of the wafer 6 by a projection magnification) is called a scanner (scanning exposure apparatus).
A kind of wafer 6 is called a second wafer already bearing a pattern. To form the next pattern on this wafer, the position of the formed pattern must be detected. This position detection method includes the TTL-AA method and OA detection method described above.
An alignment scheme having an OA detection system will be explained based on FIG. 3. As shown in FIG. 3, an OA detection system 4 is arranged separately from the projection exposure optical system 3. The wafer stage 8 is driven based on an output from an interferometer 9 capable of measuring a lateral distance. The wafer 6 is aligned in the observation region of the OA detection system 4. The OA detection system 4 detects the position of an alignment mark AM formed on the wafer 6 aligned based on the output from the interferometer 9, thereby obtaining layout information of chips (elements) formed on the wafer 6.
The wafer stage 8 is driven to the exposure region of the projection exposure optical system 3 (transfer region of the reticle) on the basis of the chip (element) layout information. Then, the wafer 6 is sequentially exposed.
A focus detection system 5 for measuring the focus direction of the projection exposure optical system 3 is generally located in the exposure region of the projection exposure optical system 3. In the focus detection system 5, a slit pattern 503 is illuminated via an illumination lens 502 with light emitted by an illumination light source 501. The light having passed through the slit pattern 503 forms the slit pattern on the wafer 6 via an illumination optical system 504 and mirror 505.
The slit pattern projected on the wafer 6 is reflected by the surface of the wafer 6, and enters a mirror 506 and detection optical system 507 arranged on a side opposite to the illumination system. The detection optical system 507 forms the slit image of the wafer 6 on a photoelectric conversion element 508 again. As the wafer 6 vertically moves, the slit image on the photoelectric conversion element 508 moves. From this moving amount, the distance of the wafer 6 in the focus direction can be measured. A plurality of such slits (points on the wafer 6) are prepared, and used one by one to detect focus positions at a plurality of positions on the wafer 6. As a result, the inclination of the wafer 6 with respect to the image plane of the reticle image of the projection exposure optical system 3 can be measured.
The OA detection system will be described with reference to the schematic view of FIG. 4.
In FIG. 4, light emitted by an illumination light source 401 (fiber or the like) is guided to a polarization beam splitter 403 via an illumination optical system 402. S-polarized light reflected by the polarization beam splitter 403 in a direction perpendicular to the sheet surface of FIG. 4 passes through a relay lens 404 and xcex/4 (quarter-wave plate) 409. Then, the S-polarized light is converted into circularly polarized light to Kxc3x6hler-illuminate the alignment mark AM on the wafer 6 via an objective lens 405.
Reflected light, diffracted light, and scattered light from the alignment mark AM return to the object lens 405 and xcex/4 plate 409, and are converted into P-polarized light parallel to the sheet surface of FIG. 4. The P-polarized light passes through the polarization beam splitter 403 and forms the image of the alignment mark AM on a photoelectric conversion element 411 (e.g., a CCD camera) via an imaging optical system 407a (407b). The position of the wafer 6 is detected based on the position of the photoelectrically converted alignment mark image.
To detect the alignment mark AM on the wafer 6 at a high precision, the image of the alignment mark AM must be clearly detected. In other words, the alignment mark AM must be adjusted to the focus surface of the OA detection system 4.
For this purpose, an AF detection system (not shown) is generally adopted. The alignment mark is detected by being driven to the best focus plane of the OA detection system on the basis of the detection result of the AF detection system.
Although a description of the TTL-AA method will be omitted, a wafer is basically observed by the OA detection system via the projection exposure optical system 3 in the TTL-AA method.
When a mark on a wafer is observed to detect the position by the above-mentioned alignment scope, monochromatic light generates interference fringes because of a transparent layer applied or formed on the mark. The alignment mark is detected while a signal of interference fringes is added to an alignment signal, failing high-precision detection. To prevent this, the light source of the alignment scope generally has wavelengths of a wide band. The alignment mark is detected as a signal almost free from interference fringes.
However, an actually manufactured alignment scope suffers aberrations due to manufacturing errors or assembly errors of optical components which constitute the alignment scope. In particular, a shift depending on the wavelength occurs owing to parallel decentering or inclination decentering of a lens or the like, and inclination decentering of a parallel plate (prism or the like). A so-called prism effect causes color smear. A shift generated for every wavelength may be enlarged by widening the wavelength band or interposing a projection exposure optical system, as described above (a shift generated by this phenomenon will be called a xe2x80x9cwavelength shiftxe2x80x9d hereinafter).
Referring back to FIG. 4, this phenomenon will be explained. The imaging optical system 407a represented by a solid line is assumed to be arranged (at the position of a design value) without any decentering from the optical axis. The imaging optical system 407b represented by a broken line is assumed to be slightly decentered from the optical axis. Decentering from the optical axis is caused by a manufacturing error, and may occur by an uncontrollable amount in an actual alignment scope.
If the lens is decentered in this manner, a so-called prism effect of the lens generates an unexpected wavelength shift. A beam Lma indicated by a solid line represents a designed beam, and a beam Lmb indicated by a broken line represents that a shift occurs by a wavelength-dependent amount owing to the prism effect.
Demerits when an alignment mark is observed by an optical system having such a wavelength-dependent shift will be described with reference to FIGS. 5 and 6.
Portion (a) in each of FIGS. 5 and 6 schematically shows the section of an alignment mark. Portion (a) in FIG. 5 shows a mark having a simple step structure, and portion (a) in FIG. 6 shows a mark having a transparent layer such as a resist (hatched portion in FIG. 6) in a step structure. The measurement direction is an X direction in FIGS. 5 and 6. Portions (b) to (d) in FIGS. 5 and 6 show waveforms of an alignment mark detected by the wavelength components of three wavelengths (first wavelength: xcex1, second wavelength: xcex2, third wavelength: xcex3) used in the alignment scope. Portion (e) in each of FIGS. 5 and 6 shows a wavelength obtained by overlapping the first to third wavelengths xcex1 to xcex3. This wavelength is one used to actually detect an alignment mark.
FIG. 5 shows detection by an alignment scope free from any wavelength shift. If no wavelength shift exists, the central positions of the waveforms of the wavelengths xcex1 to xcex3 coincide with the center of the alignment mark. The waveform ((e) in FIG. 5) of a wavelength xcex all obtained by overlapping all the wavelengths also coincides with the center of the alignment mark.
FIG. 6 shows a case wherein the alignment scope has a wavelength shift. The central position of a detected waveform shifts for every wavelength. Further, the transparent layer on the alignment mark changes the signal strength at each wavelength (e.g., the signal strength of the wavelength xcex1 shown in portion (c) of FIG. 6 decreases by a strength change xcex94I from the signal strength of the wavelength xcex1 shown in portion (c) of FIG. 5). The synthesized waveform of all the wavelengths shifts from the center of the actual alignment mark due to the central positional shift and strength difference at each wavelength. In this way, when a wavelength shift exists in the alignment scope, the signal strength weight of each wavelength changes depending on the thickness of a transparent layer, like this example. Accordingly, the shift amount may change.
For such a wavelength shift, a conventional method utilizes rotation of two wedges to adjust the wavelength shift by wavelength shifts generated by the wedges. FIG. 7 is a schematic view showing this method.
When a wavelength shift occurs in the X direction, the two wedges are rotated and adjusted around the optical axis. This rotational adjustment generates a shift xcex94 depending on the wavelength, and the wavelength shift can be corrected by xe2x88x92xcex94 generated by the entire optical system. In adjustment of rotating the wedges, however, desired adjustment is difficult because a wedge component exists also in the Y direction. Beams, which should be incident on a sensor parallel to each other, are inclined by xcex8t because they have passed through the wedges. The inclination of the beams poses a problem such as a decrease in sensor sensitivity. Further, glass portions which transmit an upper beam Lupper and a lower beam Llower change in thickness, and the focus point changes between upper and lower portions at the field angle. The entire mark region cannot be adjusted to the best focus, decreasing the position detection precision.
As a method of preventing these problems, a wavelength shift is eliminated by using the inclination of a flat glass having parallel surfaces. FIG. 12 is a schematic view for explaining this method.
To generate a large wavelength shift, an inclination angle xcex8 of a flat glass 30 having parallel surfaces must be designed to be larger, or a thickness t of the flat glass 30 must be designed to be large. Considering an actual apparatus, a large glass thickness t and a large inclination angle xcex8 pose a demerit of a bulky apparatus.
The present invention discloses an arrangement capable of correcting a wavelength shift generated by the manufacturing error of an alignment scope as described above and minimizing generation of other aberrations. It is an object of the present invention to provide a detection apparatus capable of high-precision detection.
According to a first aspect of the present invention, there is provided a detection apparatus for detecting information about a detection target by using light from the detection target, the apparatus comprising a plurality of wedge optical members, wherein the plurality of wedge optical members have at least a pair of parallel wedge surfaces facing each other, the facing wedge surfaces are inclined at a predetermined angle from a plane perpendicular to an optical axis, and the plurality of wedge optical members are arranged so as to allow adjusting an interval between the facing wedge surfaces.
According to a preferred embodiment of the present invention, the plurality of wedge optical members include first and second wedge optical member groups each constituted by at least two wedge optical systems having parallel wedge surfaces facing each other, the facing wedge surfaces of the first wedge optical member group are inclined at a first angle from the plane perpendicular to the optical axis, the facing wedge surfaces of the second wedge optical member group are inclined at a second angle from the plane perpendicular to the optical axis, and the first angle is different from the second angle.
According to a preferred embodiment of the present invention, the detection apparatus comprises an optical system group arranged so as to form an image of the detection target a plurality of number of times, and at least one of the plurality of wedge optical members is arranged on or near a plane of a highest imaging magnification among planes conjugate to a detection target plane.
According to a preferred embodiment of the present invention, at least one of the plurality of wedge optical members is arranged at a telecentric location in the detection apparatus.
According to a preferred embodiment of the present invention, the plurality of wedge optical members are so arranged as to allow adjusting the interval between the facing wedge surfaces by moving at least one of the wedge optical members in a direction parallel to a beam passing through the facing wedge surfaces.
According to a preferred embodiment of the present invention, the plurality of wedge optical members include at least two pairs of facing wedge surfaces, the first pair of facing wedge surfaces are inclined at a first angle from the plane perpendicular to the optical axis, the second pair of facing wedge surfaces are inclined at a second angle from the plane, and the first angle is different from the second angle.
According to a preferred embodiment of the present invention, the detection target includes a position detection mark formed on a substrate, and the detection apparatus further comprises a photoelectric conversion element for converting an image of the position detection mark into an electrical signal, and an optical system for imaging the position detection mark on the photoelectric conversion element.
According to a second aspect of the present invention, there is provided an exposure apparatus for transferring a pattern onto a substrate, the apparatus comprising a stage for moving the substrate and a detection apparatus for detecting information about the substrate by using light from the substrate, wherein the detection apparatus has a plurality of wedge optical members, the plurality of wedge optical members have at least a pair of parallel wedge surfaces facing each other, the facing wedge surfaces are inclined at a predetermined angle from a plane perpendicular to an optical axis, and the plurality of wedge optical members are so arranged as to allow adjusting an interval between the facing wedge surfaces.
According to a preferred embodiment of the present invention, the apparatus further comprises a display, a network interface and a computer for executing network software, and the display, the network interface, and the computer enable communicating maintenance information of the production exposure apparatus via a computer network.
According to a preferred embodiment of the present invention, the network software provides on the display the user interface for accessing a maintenance database which is provided by a vendor or user of the exposure apparatus and connected to the external network outside a factory in which the projection exposure apparatus is installed, and information is obtained from the database via the external network.
According to a third aspect of the present invention, there is provided a semiconductor device manufacturing method comprising the steps of installing, in a semiconductor manufacturing factory, manufacturing apparatuses for performing various processes including the above exposure apparatus and manufacturing a semiconductor device by performing a plurality of processes using the manufacturing apparatuses.
According to a preferred embodiment of the present invention, the method further comprises the steps of connecting the manufacturing apparatuses via a local area network; and communicating information about at least one of the manufacturing apparatuses between the local area network and an external network outside the semiconductor manufacturing factory.
According to a preferred embodiment of the present invention, a database provided by a vendor or user of the exposure apparatus is accessed via the external network, thereby obtaining maintenance information of the manufacturing apparatus by data communication, or data communication is performed between the semiconductor manufacturing factory and another semiconductor manufacturing factory via the external network, thereby performing production management.
According to a fourth aspect of the present invention, there is provided a semiconductor manufacturing factory comprising manufacturing apparatuses, for performing processing, including the above exposure apparatus, a local area network for connecting the manufacturing apparatuses, and a gateway for allowing access to an external network outside the factory from the local area network, wherein information about at least one of the manufacturing apparatuses is communicated.
According to a fifth aspect of the present invention, there is provided a maintenance method for the above exposure apparatus, which is installed in a semiconductor manufacturing factory, the method comprising the steps of making a vendor or user of the production exposure apparatus provide a maintenance database connected to an external network of the semiconductor manufacturing factory, allowing access to the maintenance database from the semiconductor manufacturing factory via the external network, and transmitting maintenance information accumulated in the maintenance database to the semiconductor manufacturing factory via the external network.
According to a sixth aspect of the present invention, there is provided an adjustment method for a detection apparatus for detecting information about a detection target by using light from the detection target, wherein the detection apparatus has a plurality of wedge optical members, the plurality of wedge optical members have at least a pair of parallel wedge surfaces facing each other, the facing wedge surfaces are inclined at a predetermined angle from a plane perpendicular to an optical axis, and the method comprises the step of adjusting an interval between the facing wedge surfaces.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.